This invention relates to modem architecture for communication lines. More particularly, this invention relates to modem circuitry used in connection with isolation systems for connecting to phone lines.
New generations of consumer appliances like set-top boxes, payphones, vending machines and other systems often require or prefer low-speed data modems. Such modems allow remote hosts to handle billing or other housekeeping functions, or permit xe2x80x9csmartxe2x80x9d vending machines to call for more supplies. Although typical microprocessor and digital-signal-processor (DSP)-based multimedia chips employed in set-top boxes and other systems are capable of implementing a low-speed modem, they would do so at an undesirable manufacturing complexity and expense.
Prior modem architectures typically included multiple integrated circuits for handling modem processing and communication line termination. In particular, one or more digital-signal-processor chips have been coupled to analog-front-end circuitry, which in turn has been connected to line termination circuitry across a transformer isolation barrier. Such modem architectures suffer from numerous disadvantages.
The present invention provides an improved modem architecture and associated method that integrate modem functionality and line-side isolation functionality while also providing a modem interface that allows raw data, such as raw pulse-code-modulated (PCM) data, or modem data to be selectively communicated through a serial interface.
In one embodiment, the present invention is an integrated modem and line-isolation circuit including system-side line-isolation circuitry capable of being coupled to an isolation barrier to communicate digital information through the isolation barrier, digital signal processing (DSP) circuitry integrated with the system-side line-isolation circuitry having a modem processor for modem data and a digital processor for system-side circuitry, and a serial interface through which modem data from the modem processor or raw data from the digital processor may be selectively communicated. In a more particular embodiment, the raw data may be pulse-code-modulated (PCM) data. Still further, the PCM data may be M-bit PCM data evenly separated into a plurality of N-bit data words. In addition, an X-bit control word may be sent or received with each N-bit PCM data word so that the X-bit control words identify how the N-bit PCM data words are combined to form M-bit PCM data.
In further embodiments, a start bit may be sent or received before each N-bit PCM data word and each associated X-bit control word, and a stop bit may be sent or received after each N-bit PCM data word and each associated X-bit control word. The serial interface may also be an asynchronous serial interface. Furthermore, the serial interface may include at least one serial input pin through which PCM data may be received, and the modem interface may further include a control pin through which a timing signal may be sent when the serial input pin is receiving PCM data, wherein the timing signal indicates readiness for receipt of data.
In still another embodiment, the present invention is a method for sending raw data or modem data across a serial interface of an integrated modem and line-isolation circuit including providing a system-side line-isolation integrated circuit having digital-signal-processing (DSP) circuitry with a modem processor for modem data and a digital processor for system-side circuitry, providing a serial interface, and selectively communicating modem data from the modem processor or raw data from the digital processor through the serial interface. In a more particular embodiment, the raw data is pulse-code-modulated (PCM) data.